1. Field of the Invention
The present invention relates to an algorithm for a decoder used in a transmission channel, particularly to a set-cyclic comparison method for an LDPC decoder.
2. Description of the Related Art
Distinct from general source coding, error control coding is used to restore as much as possible of the data damaged in transmission by the poor reliability of the transmission medium or the interference of external factors. Among error control codes, the low-density parity-check (LDPC) code is a promising and very useful coding technology.
An LDPC decoder may adopt a sum-product algorithm or a min-sum algorithm to perform decoding. The sum-product algorithm can reduce the complexity of calculation; however, it consumes more hardware resources. Thus, an LDPC decoder usually adopts the min-sum algorithm to reduce the complexity of hardware.
Refer to FIG. 1 a flowchart of the decoding process of an LDPC decoder. As shown in FIG. 1, the decoder is initialized firstly in Step S10; next, check nodes and bit nodes are respectively updated in Step S12 and Step S14; then, in Step S16, it is checked whether the iteration number of the data lists exceeds a predetermined maximum iteration number or whether the decoded information bits satisfies the check matrix constraint: HxT=0; if the result is positive, the decoded bits are output, and the process ends, as shown in Step S18; if the result is negative, the process returns to Step S12 to repeat the updates of the check nodes and the bit nodes.
The updates of the check nodes and the bit nodes are implemented with a check node unit (CNU) and a bit node unit (BNU). Therefore, CNU and BNU have great influence on the performance of the decoder. The conventional technologies cannot apply to a CNU with an arbitrary input number but can only get an optimal result for a specified input number. In the conventional technologies, the greater the input number, the more the comparison operations. Thus, the comparators need increasing, and the CNU operation speed slows down, and the performance of the decoder is degraded.
Accordingly, the present invention proposes a set-cyclic comparison method for an LDPC decoder to solve the abovementioned problems.